1. Field of the Invention
The present invention relates to an automatic workpiece transport apparatus for loading and unloading workpieces such as semiconductor substrates into and from a double-side polishing machine in which both sides of the semiconductor substrates are polished simultaneously.
2. Description of the Related Art
Conventionally, a double-side polishing machine has been used for simultaneously polishing both sides of workpieces such as semiconductor substrates. In such a polishing machine, carriers each having a plurality of workpiece holders in the shape of a circular hole are in meshing engagement with a sun gear and an internal gear, and semiconductor substrates are placed in the workpiece holders. The semiconductor substrates are sandwiched between an upper and lower polishing turn tables to be held thereby, and upon rotation of the sun gear etc., the carriers cause sun-and-planet motion. Simultaneously with this, the upper and lower polishing turn tables are rotated in opposite directions in order to simultaneously polish both sides of the semiconductor substrates. Also, there has been known a method for loading and unloading workpieces into and from such carriers, e.g., a method used in an automatic surface polishing apparatus disclosed in Japanese Patent Publication Laid-Open (kokai) No. 61-241060.
In the method, loading and unloading of workpieces onto and from carriers are performed on a stage outside the polishing machine, and subsequently, a robot arm is operated to transport the carriers and workpieces together onto the polishing machine.
However, in the above-described conventional polishing apparatus, since mistakes in relation to transport of the workpieces into the carriers and transport of the carriers cannot be detected, an operator may start a polishing operation without being aware of such mistakes, resulting in generation of failed products.